1. Field of the Invention
This invention relates to a lens mounting for film recording camera or magnetic recording medium camera, and, more particularly, to a lens mounting having a built-in motor for driving a diaphragm device therein.
2. Description of the Prior Art
Previous proposals for incorporating a motor within the outer lens barrel so that the diaphragm device or a lens component in the lens mounting is driven by that motor are known in, for example, U.S. Pat. Nos. 4,100,558 and 4,152,060. In order to transmit motion of the motor to the diaphragm device (diaphragm blades), for example, a drive connection between the rotor of the motor and the diaphragm blades can be employed. In this case, however, it is necessary that rotation of the rotor unit be good in stability and quietness. But, the conventional motor built in lens mountings have not ever been improved by paying attention to this point.
Documents concerning the prior-known bearing for the rotor unit may be Japanease Laid-Open Patent Application Nos. SHO 57-165825 and SHO 57-166847, in which the rotor unit and the bearing mechanism are constructed in separate form from each other. To assemble the rotor unit with the bearing mechanism, difficult problems have arisen in the design and in the assembly line, when the number of parts increases and the complexity of structure increases.
Recently, plastic molding techniques have found increased use in making up rotors of plastic magnet, and there have been previous proposals for using these plastic magnets in the motor of the lens mounting as disclosed in U.S. patent application Ser. Nos. 611,413 and 688,365.
It is also known to provide a technique of using a stepping motor for controlling the opening and closing operation of the diaphragm blades, as in Japanese Laid-Open Utility Model Applications Nos. SHO 56-32823 and 56-32824.